首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   924篇
  免费   74篇
  国内免费   1篇
电工技术   6篇
化学工业   485篇
金属工艺   25篇
机械仪表   11篇
建筑科学   23篇
矿业工程   3篇
能源动力   18篇
轻工业   148篇
水利工程   2篇
石油天然气   18篇
无线电   49篇
一般工业技术   104篇
冶金工业   48篇
原子能技术   3篇
自动化技术   56篇
  2024年   2篇
  2023年   18篇
  2022年   140篇
  2021年   141篇
  2020年   46篇
  2019年   37篇
  2018年   36篇
  2017年   36篇
  2016年   45篇
  2015年   30篇
  2014年   32篇
  2013年   56篇
  2012年   52篇
  2011年   58篇
  2010年   32篇
  2009年   22篇
  2008年   23篇
  2007年   25篇
  2006年   19篇
  2005年   12篇
  2004年   12篇
  2003年   10篇
  2002年   13篇
  2001年   8篇
  1999年   4篇
  1998年   3篇
  1997年   3篇
  1995年   2篇
  1994年   4篇
  1992年   2篇
  1991年   5篇
  1990年   4篇
  1989年   4篇
  1988年   3篇
  1987年   3篇
  1986年   4篇
  1985年   2篇
  1984年   2篇
  1983年   2篇
  1982年   4篇
  1981年   2篇
  1980年   2篇
  1979年   4篇
  1977年   5篇
  1976年   6篇
  1974年   2篇
  1973年   3篇
  1972年   4篇
  1970年   2篇
  1969年   4篇
排序方式: 共有999条查询结果,搜索用时 18 毫秒
51.
This study aimed to develop and characterize gelatin/polyvinyl alcohol (G/PVA) films loaded with black cumin cake extract (BCCE) and zinc oxide nanoparticles (ZnONPs). The BCCE was also applied for the green synthesis of ZnONPs with an average size of less than 100 nm. The active films were produced by a solvent-casting technique, and their physicochemical and antibacterial properties were investigated. Supplementation of G/PVA film in ZnONPs decreased the tensile strength (TS) from 2.97 MPa to 1.69 MPa. The addition of BCCE and ZnONPs increased the elongation at the break (EAB) of the enriched film by about 3%. The G/PVA/BCCE/ZnONPs film revealed the lowest water vapor permeability (WVP = 1.14 × 10−9 g·mm·Pa−1·h−1·mm−2) and the highest opacity (3.41 mm−1). The QUick, Easy, New, CHEap and Reproducible (QUENCHER) methodologies using 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6- sulfonic acid) (ABTS) and cupric ion reducing antioxidant capacity (CUPRAC) were applied to measure antioxidant capacity (AC) of the prepared films. The incorporation of BCCE and ZnONPs into G/PVA films enhanced the AC by 8–144%. The films containing ZnONPs and a mixture of BCCE and ZnONPs inhibited the growth of three Gram-positive bacterial strains. These nanocomposite films with desired functional properties can be recommended to inhibit microbial spoilage and oxidative rancidity of packaged food.  相似文献   
52.
53.
Spin valves that comprise synthetic antiferromagnet as a component of pinned layer and an exchange-coupled ferromagnet/Ru/ferromagnet structure in the free layer have been prepared by magnetron sputtering. Microobjects have been formed from spin valves by optical and electron-beam lithography. It has been shown that the shift of the low-field magnetoresistance hysteresis loop decreases as the thicknes of the Ru spacer in the free layer of spin valve increases. The almost hysteresis-free odd-field dependences of the magnetoresistance were obtained for micron-sized samples; in this case, the sensitivity is 0.2%/Oe.  相似文献   
54.
Magnesium doped lanthanum ortho-niobate (La0.98Mg0.02NbO4) was prepared by the molten salt synthesis method. X-ray diffraction and dilatometry methods were used to study high temperature behavior of the ceramic material. Special attention was paid to the phase transition between the monoclinic and tetragonal phases. The values of spontaneous strain on the basis of unit cell parameter, obtained by Rietveld refinement, have been calculated as well as Landau order parameter. The thermal expansion coefficient (TEC) of La0.98Mg0.02NbO4 was determined to be 12×10?6 1/K and 8×10?6 1/K below and above 500 °C, respectively.  相似文献   
55.
Embodied conversational agents (ECAs) are computer-generated, human-like characters that interact with human users in face-to-face conversations. ECA is a powerful tool for representing cultural differences and is suitable for interactive training or edutainment systems. This article presents preliminary results from the development of a culture-adaptive virtual tour guide agent for serving Japanese, Croatian, and general Western users by displaying appropriate verbal and non-verbal behaviors. It is being implemented in Generic ECA Framework, a modular framework for developing ECAs. Dividing the ECA functions into reusable and loosely coupled modules minimizes the effort required to implement additional behavior and facilitates incremental scale up of the system.  相似文献   
56.
BACKGROUND: Bioethanol is mostly produced from starchy parts of the corn grain kernel leaving significant amounts of valuable by‐products such as dried distillers' grains with solubles (DDGS) which can be used as a substitute for traditional feedstuff. The suitability of six maize hybrids from Serbia was investigated for bioethanol and DDGS production. The correlation between physical and chemical characteristics of the grain, bioethanol yield and quality of the corresponding DDGS was assessed. RESULTS: All hybrids had very different chemical composition and physical characteristics which could allow various applications. The highest bioethanol yield (94.5% of theoretical) and volumetric productivity (2.01 g l?1 h?1) were obtained with hybrid ZP 434 and the lowest with ZP 611k. Regarding chemical composition, all DDGS samples manifested good properties as feed components. Their protein content was higher compared to the kernel. In addition, the samples showed high digestibility and high mineral content, especially of calcium and phosphorus. CONCLUSION: A hybrid ZP 434 was selected as the most promising bioethanol producer. This property is attributed to the highest level of soft endosperm which is more susceptible to starch‐hydrolysing enzymes. A high yield potential per hectare makes it the best candidate for commercial bioethanol production. © 2012 Society of Chemical Industry  相似文献   
57.
The greenhouse gas mitigation potential of different economic sectors in three world regions are estimated using a bottom-up approach. These estimates provide updates of the numbers reported in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4). This study is part of a larger project aimed at comparing greenhouse gas mitigation potentials from bottom-up and top-down approaches. The sectors included in the analysis are energy supply, transport, industry and the residential and service sector. The mitigation potentials range from 11 to 15 GtCO2eq. This is 26–38% of the baseline in 2030 and 47–68% relative to the year 2000. Potential savings are estimated for different cost levels. The total potential at negative costs is estimated at 5–8% relative to the baseline, with the largest share in the residential and service sector and the highest reduction percentage for the transport and industry sectors. These (negative) costs include investment, operation and maintenance and fuel costs and revenues at moderate discount rates of 3–10%. At costs below 100 US$/tCO2, the largest potential reductions in absolute terms are estimated in the energy supply sector, while the transport sector has the lowest reduction potential.  相似文献   
58.
We have compared the results of estimations of the total number of protein-coding genes in the Saccharomyces cerevisiae genome, which have been obtained by many laboratories since the yeast genome sequence was published in 1996. We propose that there are 5300-5400 genes in the genome. This makes the first estimation of the number of intronless ORFs longer than 100 codons, based on the features of the set of genes with phenotypes known in 1997 to be correct. This estimation assumed that the set of the first 2300 genes with known phenotypes was representative for the whole set of protein-coding genes in the genome. The same method used in this paper for the approximation of the total number of protein-coding sequences among more than 40 000 ORFs longer than 20 codons gives a result that is only slightly higher. This suggests that there are still some non-coding ORFs in the databases and a few dozen small ORFs, not yet annotated, which probably code for proteins.  相似文献   
59.
Progressive systemic sclerosis may be associated with focal myocardial fibrosis. Electrocardiographic abnormalities including conduction block are common in progressive systemic sclerosis but whether they are due to direct destruction of the specialized conduction tissue of the heart is uncertain. The conduction systems of 35 patients with progressive systemic sclerosis were studied. Of these 35 patients, 17 (50 per cent) had myocardial fibrosis of the type seen in progressive systemic sclerosis. In 10 of the 17, it was severe. Sinus node fibrosis was present in 13 patients and was nearly as frequent in those with as in those without the progressive systemic sclerosis myocardial lesion. Overlying pericarditis may have contributed to the fibrotic changes within the sinoatrial nodes in seven of the 13 patients. The atrioventricular node and main His bundles were normal. However, fibrotic changes were found in the proximal bundle systems in six patients. In three of the six, severe myocardial progressive systemic sclerosis was present, two had focal fibrous atrophy of the left bundle, and one had complete interruption of the right bundle. In only the latter patient was this reflected in the electrocardiogram which showed a right bundle branch block. Three patients without progressive systemic sclerosis myocardial lesions also had fibrous atrophy of a portion of the proximal left bundle branch, and in one the electrocardiogram showed an isolated left anterior hemiblock. Thus, morphologic abnormalities within the conduction system in our patients are difficult to attribute to progressive systemic sclerosis per se. Furthermore, although conduction abnormalities were more frequent in patients with myocardial disease, specific conduction system disease was not the cause in most patients. As has been noted in ischemic heart disease, the conduction system appears to be relatively spared from the myocardial changes of progressive systemic sclerosis, and the high incidence of conduction disturbances in this condition may be a consequence, rather, of damage to working myocardium.  相似文献   
60.
A method for determining the concentration of active microbial biomass in granular activated carbon (GAC) filters used in water treatment was developed to facilitate studies on the interactions between adsorption processes and biological activity in such filters. High-energy sonication at a power input of 40 W was applied to GAC samples for the detachment of biomass which was measured as adenosine triphosphate (ATP). Modelling of biomass removal indicated that a series of six to eight sonication treatments of 2 min each yielded more than 90% of the attached active biomass. The ATP concentrations in 30 different GAC filters at nine treatment plants in The Netherlands ranged from 25 to 5000 ng ATP cm(-3) GAC, with the highest concentrations at long filter run times and pretreatment with ozone. A similar concentration range was observed in nine rapid sand (RS) filters. ATP concentrations correlated significantly (p<0.05) with total direct bacterial cell counts in each of these filter types, but the median value of the ATP content per cell in GAC filters (2.1 x 10(-8) ng ATP/cell) was much lower than in the RS filters (3.6 x 10(-7) ng ATP/cell). Average biofilm concentrations ranging from 500 to 10(5) pg ATP cm(-2) were calculated assuming spherical shapes for the GAC particles but values were about 20 times lower when the surface of pores >1 microm diameter is included in these calculations. The quantitative biomass analysis with ATP enables direct comparisons with biofilm concentrations reported for spiral wound membranes used in water treatment, for distribution system pipes and other aquatic environments.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号